The present invention relates to a process for contacting gas and liquid, as applied in processes of mass and heat exchange and in particular in such operations, for the distillation, rectification, extraction, absorption, desorption, drying and humidification of gas, as well as for its dedusting.
The invention relates also to the packing employed in such processes, which packing constitutes a substantial part of the columns.
Processes of mass and heat exchange, consisting in the formation of gas and liquid streams in columns provided with packing, run as a general rule in counter-current motion.
In this known and presently used method of a diaphragmic mass and heat exchange, the exchange is carried out by the contact of gas with a film of the liquid in counter-current motion. Liquid flows down the walls of the column and along the surface of the packing device, contacting the gas which flows upwardly. The contact of phases takes place on the surface of the film of the liquid, the contact time being, on account of the counter-current motion, very short. The duration of the contact time of the phases, as well as the interfacial surface are in this situation dependent upon the configuration of the surface of the packing elements.
Excessive enlargement of this surface is however limited by the increase of the resistance of flow.
The packings used until now are based on the principle of maximum development of the surface in order to obtain intensive mass and heat exchange. For industrial purposes the following are used standard packings: Raschig rings, Berl saddles or Intalox, improved standard packings, such as rings with a cut-out Bialecki, Pall, perforated rings, Cannon and especially shaped pieces Interpax, Stadman, Sulzer.
The most compact structures show packings made of horizontal and vertical sheet packs or tubes, characterized by a uniform contact of liquid and gas phases, in cross-section where the packings are vertical or horizontal sheets, the liquid flows down in a thin layer and the contact of phases takes place on its surface. In one variation chequerwork packings are used, their operation being similar to that of sieve plates. They are made of perforated sheets bent and put together in a way to form channels of a square section. Liquid flows down the walls, mixing with the gas stream.
There is also known a cell packing in the shape of a lattice, forming cells in square section. The cells are bent in their lower part to form a slit through which gas flows in which the cells break the liquid stream, thus increasing the contact surface.
All of the solutions applied until now show a number of imperfections and inconveniences.
Thus, the standard packing has a low elasticity resulting from the possibility of flooding caused by the lack of an overall surface sprinkling and by the so called "channeling" effect. Improved standard packings enable increase loadings, but show a two-fold or a three-fold increase in resistance to flow in comparison with standard packings, and because of their more complicated shape they are more difficult to make.
Pack packings, in comparison to standard packings, enable increase loadings, improve the contact of phases, obtain higher rates and reduce the resistance of flow. Because shapes are, however, more complicated, they are much more difficult to make.
The construction of cell packings with elements open at the top and with a slit in their lower part is simple, creating the possibility of obtaining, in industrial application gas velocities up to 5 m/Sec. calculated upon an empty section, at low resistances of flow.
This packing permits, however, agitation of the gas stream only inside the cell and breaks the liquid stream. Excessive loadings of gas and liquid force the liquid out of the cells or cause the floating of a foam layer over the packing, leading thus to the reduction of the contact time between the streams.
The object of the present invention is to extend the contact time of gas and liquid and to increase simultaneously the interfacial surface without the necessity of overdeveloping the packing surface.